We have treated the economy as a machine. Instead, Roger Martin, a former dean of the Rotman School of Management, contends in an important new book , it is “a complex adaptive system — one that is too complex to be perfectible, one that continuously adapts in ways that will almost certainly frustrate any attempts to engineer it for perfection”. Solutions to the endemic efficiency problem include recognising that “slack is not the enemy”. That is a bitter lesson that health systems, companies and individuals learnt only when their lack of economic resilience was tested by sudden lockdown.